Technical Abstract:
Allowing the sugarcane post-harvest residue blanket to remain on the field often reduces ratoon crop yields in temperate climates such as Louisiana. This article outlines the progress of our residue management research focused on reducing the need for burning in Louisiana sugarcane production. Some of our first efforts were to increase the decomposition of the residue layer in the field by the addition of biological or chemical adjuvants applied in the fall/early winter. The addition of the bacterial and fungal consortium to the residue did not increase decomposition or increase yields. However, the application of UAN at a rate of 67 kg N/ha was found to increase gross cane yield sufficiently to circumvent the yield depressions caused by the residue with LCP 85-384. Another set of studies focused on the effect of different residue removal methods and removal timings on the growth and yield of the subsequent ratoon crop. Tests were conducted on first, second, and third ratoon LCP 85-384 on heavy and light soils. Burning, repositioning residue from the row top to the wheel furrow, and full residue retention were evaluated. For all ratoon-crop sugar yields, burning and mechanical removal between October and January resulted in an average of 500 kg/ha more sugar than with full retention. When the experiment was repeated on newer varieties including HoCP 96-540, L 99-226, and HoCP 00-950 mechanical removal did not result in sugar yields equivalent to burning. HoCP 96-540 and L 99-226 appear to be very sensitive to saturated soils which can occur if the residue repositioned into the wheel furrow impedes drainage. In addition to cultural practices for residue management, USDA scientists are screening germplasm for early spring emergence through the residue blankets. Preliminary results indicate that certain clones are tolerant to the residue and achieve similar yields with or without the residue blanket present. The challenge is that this basic germplasm has lower sucrose concentrations than the commercial standards. All currently planted commercial varieties have also been screened for residue tolerance. We have determined differences in tolerance to the blanket of residue among the existing commercial varieties, with L 99-233 showing the greatest tolerance relative to LCP 85-384, Ho 95-988, HoCP 96-540, L 97-128, L 99-226, HoCP 00-950, and L 01-283. This may be a niche variety to plant in sensitive areas where burning is not an option. We are currently evaluating new varieties and advanced lines for residue tolerance to ultimately provide multiple varieties with tolerance to post-harvest residue.